1. Field of the Invention
The present invention generally relates to heat transfer including the transportation of heat energy. More specifically, the present invention is related to heating, ventilation, and air conditioning (HVAC) applications, especially liquid heating and cooling.
2. Description of the Related Art
There are many applications where it is desirable to move heat energy. For example, in the field of air-conditioning, heat energy is moved either out of or into a body of air within a building, vehicle, or other enclosed space. Such systems generally operate in the context of the co-efficient of performance (COP)—the ratio of the energy gained by the body of air relative to the energy input. Many air conditioning systems operate with a COP of 2 to 3.5.
Water heating also invokes various heat transportation applications. Many water heating systems rely upon the direct application of heat energy to a body of water in order to raise temperature. As a result, the COP of such systems is usually limited to 1. While water heating systems could theoretically be devised utilizing certain operating principles of air conditioning and refrigeration systems, the increased capital expenses of such a system typically are not justified by the corresponding gain in performance.
A vapor compression system, as found in many air-conditioning applications, generally includes a compressor, a condenser, and an evaporator. These systems also tend to include an expansion device. In a prior art vapor compression system, a gas is compressed whereby the temperature of that gas is increased beyond that of the ambient temperature. The compressed gas is then run through a condenser and turned into a liquid. The condensed and liquefied gas is then taken through an expansion device, which drops the pressure and the corresponding temperature. The resulting refrigerant is then boiled in an evaporator.
FIG. 1 illustrates a vapor compression system 100 as might be found in the prior art. In the prior art vapor compression system 100 of FIG. 1, compressor 110 compresses the gas to (approximately) 238 pounds per square inch (PSI) and a temperature of 190° F. Condenser 120 then liquefies the heated and compressed gas to (approximately) 220 PSI and 117° F. The gas that was liquefied by the condenser 120 is then passed through the expansion valve 130 of FIG. 1. By passing the liquefied gas through expansion value 130, the pressure is dropped to (approximately) 20 PSI.
A corresponding drop in temperature accompanies the drop in pressure, which is reflected as a temperature drop to (approximately) 34° F. in FIG. 1. The refrigerant that results from dropping the pressure and temperature at the expansion value 130 is boiled at evaporator 140. Through boiling of the refrigerant by evaporator 140, a low temperature vapor results. Said vapor is illustrated in FIG. 1 as having (approximately) a temperature of 39° F. and a corresponding pressure of 20 PSI.
The cycle related to the system 100 of FIG. 1 is sometimes referred to as the vapor compression cycle. Such a cycle generally results in a COP between 2.4 and 3.5. The COP, as reflected in FIG. 1, is the evaporator cooling power or capacity divided by compressor power. It should be noted that the temperature and PSI references that are reflected in FIG. 1 are exemplary and for the purpose of illustration.
FIG. 2 illustrates the performance of a vapor compression system similar to that illustrated in FIG. 1. The COP illustrated in FIG. 2 corresponds to a typical home or automotive vapor compression system (like that of FIG. 1) with an ambient temperature of (approximately) 90° F. The COP shown in FIG. 2 further corresponds to a vapor compression system utilizing a fixed orifice tube system.
A system like that described in FIG. 1 and further referenced in FIG. 2 typically operates at an efficiency rate or COP that is far below that of system potential. To compress gas in a conventional vapor compression system like that illustrated in FIG. 1 (100) typically takes 1.75-2.5 kilowatts for every 5 kilowatts of cooling power. This exchange rate is less than optimal and directly correlates to the rise in pressure times the volumetric flow rate. Degraded performance is similarly and ultimately related to performance (or lack thereof) by compressor 110.
Haloalkane refrigerants such as tetrafluoroethane (CH2FCF3) are inert gases that are commonly used as high-temperature refrigerants in refrigerators and automobile air conditioners. Tetrafluoroethane has also been used to cool over-clocked computers. These inert, refrigerant gases are more commonly referred to as R-134 gases. The volume of an R-134 gas can be 600-1000 times greater than the corresponding liquid, which evidences the need for an improved vapor compression system that more fully recognizes system potential and overcomes technical barriers related to compressor performance.